The present invention relates to orthopedic devices for surgical treatment of bone fractures and for the prophylactic treatment of pathological bones, and more particularly to expandable intramedullary devices, and to methods for making and using such devices.
Fractures of limb bones have been treated with internal fixation devices, such as plates lying on the surface of a bone, nails running inside the medullary canal of a fractured bone, and/or screws affixing both ends of a fractured bone together. These internal fixation devices may provide reasonable structural rigidity and/or stability to the fractured bone without compromising some of the strain desired to stimulate bone cells.
An intramedullary fixation method is a traditional procedure for treating long bone fractures, affixing the bone fracture using intramedullary nails, without disturbing the periosteum of the bone. Such a method may be accomplished in a closed manner, and the fractured bone may be functionally used (including weight bearing) during healing. The surgical approach for insertion of intramedullary nails varies slightly for each bone and is well described in the orthopedic literature.
Some of the problems associated with conventional intramedullary fixation methods include lack of rotation stability, collapse of the fracture site in some fracture types, and/or undesired backup of nails. Furthermore, although the actual shape of the bone typically includes some degree of curvature, the intramedullary nails used to mend the fractured bone are generally straight. Still further, intramedullary fixation methods may introduce interlocking screws across the nail, creating some disadvantages. Specifically, conventional intramedullary fixation nails for long bones may include a rigid structure (hollow or full), that may be locked at their extremes by the addition of screws transversally applied through the bone walls and the nail itself. This additional step generally makes the operation longer and more complicated, and may require additional skin incisions and/or longer use of an image intensifier (X-ray). Furthermore, undesired gaps between the bone ends may originate from the screws, which are permanent unless removed in a new operation. Also, the resultant structure in certain situations may be too stiff and may lack desired elasticity. In contaminated fractures, metallic intramedullary nails may propagate contamination through the entire canal, despite attempts at cleaning the fracture site, which may lead to bone infection.
Recent developments in the intramedullary fixation approach have attempted to address some of these problems. For example, PCT Publication No. WO 98/38918 to Beyar suggests three structural designs: (1) a solid metal sheet that expands in the medullary canal; (2) a meshwork structure consisting of ribs circumferentially connected at the tips; and (3) a balloon structure that is inflated once inserted into the medullary canal. The first two structures, however, may not provide firm support within the metaphysis of the bone. Specifically, these structures are unable to expand at their ends, because the total expansion of the structures is limited by the circumference of the diaphyseal segment of the medullary canal. The balloon structure also has limited utility because, when inflated, it may disrupt blood supply of the bone and prevent regeneration or recovery, and/or may not be adjustable to changes in the shape of the medullary canal, because of its set volume once inserted and inflated.
U.S. Pat. No. 5,281,225 to Vicenzi discloses a structure that includes a multitude of elastically deformable stems connected together by a stub. When inserted in the medullary canal of a fractured bone, the distal tips of the stems expand outward into the end of the medullary canal to anchor the Vicenzi structure within the bone. This device, however, is a passive device, expanding automatically upon deployment, and may not be controllably expanded. Additionally, the Vicenzi structure is not expanded within the medullary canal and, thus, does not provide multiple points of contact with the wall of the medullary canal. As a result, the Vicenzi structure may not ensure structural stability along the transversal and rotational planes of the fractured bone.
Accordingly, intramedullary devices that provide and/or ensure stability to a fractured one would be considered useful.
The present invention is directed to orthopedic devices for surgical treatment of bone fractures and for the prophylactic treatment of pathological bones, and more particularly to expandable intramedullary devices, and to methods for manufacturing and implanting them.
According to a first aspect of the present invention, a device for stabilizing bone includes an elongate body having first and second end regions defining a longitudinal axis therebetween. A plurality of splines extend from the first end region, the splines including first ends coupled to the first end region of the elongate body, and second ends disposed away from the first end region, the second ends of the splines being directable from a generally axial collapsed state to a substantially transverse expanded state. Support arms are coupled to the splines, and an actuator is coupled to the support arms, the actuator movable axially relative to the elongate body for causing the support arms to direct the second ends of the splines from the collapsed state to the expanded state.
In one embodiment, the elongate body is a tubular shaft including a lumen extending between the proximal and distal end regions, and the actuator includes an elongate member received within the lumen, and preferably slidably coupled to the tubular shaft by mating threaded regions. A collar is coupled to the elongate member and to the support arms. Preferably, the elongate member includes a threaded region over which the collar is threaded such that rotation of the elongate member relative to the tubular shaft causes the collar to move axially, thereby causing the support arms to direct the splines between the collapsed and expanded states.
In accordance with another aspect of the present invention, a device for stabilizing bone includes an elongate body having first and second end regions defining a longitudinal axis therebetween, and an intermediate region between the first and second end regions. A first plurality of splines extend from the first end region, the splines being directable from a generally axial collapsed state to a substantially transverse expanded state. A second plurality of splines extend from a region of the elongate body distal to the proximal end region, the splines being directable from a generally axial collapsed state to a substantially transverse expanded state.
First and second pluralities of support arms are coupled to the first and second plurality of splines, respectively, and an actuator is coupled to the support arms. The actuator is movable axially relative to the elongate body for causing the first and second pluralities of support arms to direct the splines between the collapsed and expanded states.
Preferably, the elongate body is a tubular shaft including a lumen extending between the proximal and distal end regions, and the actuator includes an elongate member received within the lumen. First and second collars are coupled to the elongate member and to the first and second pluralities of support arms, respectively. Rotation of the elongate member relative to the tubular shaft causes the first and second collars to move axially, thereby causing the first and second pluralities of support arms to direct the splines between the collapsed and expanded states.
In one embodiment, the second plurality of splines extend distally from the distal end region of the tubular shaft. The elongate member may include first and second threaded regions having thread patterns that are opposite hand relative to one another. The first and second collars are threadably coupled to the first and second threaded regions, respectively. Because of the opposite hand thread arrangement, rotation of the elongate member may cause the collars to move in opposite directions. Thus, rotating the elongate member in a first direction may cause the collars to move away from one another to expand the splines, while rotating the elongate member in the opposite direction may cause the collars to move towards one another and collapse the splines.
In an alternative embodiment, the second plurality of splines may be located on the intermediate region of the tubular shaft. In a further alternative, additional sets of splines may be located along the tubular shaft in addition to those described above. Thus, a single actuator may be used to expand multiple sets of splines on a single device. The splines may have differing shapes and/or lengths, thereby enabling the device to be implanted within a bone cavity having a predetermined shape.
Optionally, an axial extension may be provided in a device in accordance with the present invention, e.g., extending proximally from the proximal end of the device beyond the splines. For example, the elongate member may be extended proximally beyond the splines on the first end of the tubular shaft, or the tubular shaft itself may include an extension. Holes may be provided in the axial extension through which nails, screws, or other fixation elements may be received to provide additional transverse support. In a further option, an indicator element may extend proximally from the device or the elongate member may be extended to facilitate location of the device after implantation.
In accordance with yet another aspect of the present invention, a method is provided for making a device for stabilizing bone. An elongate tubular shaft is provided including first and second end regions defining a longitudinal axis therebetween. Splines are formed having first ends remaining attached to the first end region of the tubular body and second ends disposed axially relative to the first ends, the second ends being freely movable relative to the tubular body. Preferably, the splines are formed by creating longitudinal slots in the first end region. Support arms are formed in the splines, the support arms having first ends that are freely movable relative to the splines and second ends remaining attached to the splines. Preferably, the support arms are formed by partially cutting away portions of respective splines.
The first ends of the support arms may be coupled to an actuator, and the actuator may be movable axially relative to the tubular shaft for buckling the support arms transversely outward relative to the longitudinal axis, thereby directing the second ends of the splines transversely outward. In a preferred embodiment, the actuator includes an elongate member and a first collar. The elongate member may be inserted into an axial lumen in the tubular shaft, and the first collar may be threaded over the elongate member until the collar is proximate the first ends of the support arms. The first ends of the support arms may then be coupled to the first collar.
In a preferred embodiment, the tubular shaft includes an internal threaded portion within the lumen, and the elongate member also includes a mating threaded region that slidably engages the threaded portion of the tubular shaft. Thus, axial movement of the elongate member relative to the tubular shaft may be limited except upon controlled rotation of the elongate member.
Optionally, a second set (or additional sets) of splines and support arms may be formed on other regions of the tubular shaft, e.g., on one of the second end region or an intermediate region of the tubular shaft. In this case, a second collar may be threaded over the elongate member until the second collar is proximate the second set of support arms, and the second set of support arms coupled to the second collar.
A device in accordance with the present invention may be inserted through an entry portal previously formed using conventional procedures, e.g., into a medullary canal of a bone, such as the femur, with the splines collapsed. Preferably, a guidewire is first introduced through the entry portal into the medullary canal of the bone using conventional methods and extended to a distal segment of the bone. The device may then be advanced over the guidewire into the medullary canal. After insertion of the device, the guidewire may be removed.
Once the device is fully inserted within the medullary canal, the actuator may be activated, e.g., using a tool inserted into the entry portal, to expand the splines to the expanded state such that the splines substantially engage internal bone or other tissue, thereby substantially anchoring the device relative to the bone. Thus, the device may prevent segments of a fractured bone within which the device is implanted from moving axially, bending, and/or rotating relative to one another. Optionally, if additional stability is desired, an extension may be provided that extends beyond the splines, and fixation devices, e.g., screws or nails, may be introduced transversely into the bone, and through holes in the extension to further secure the segments of bone.
After the fracture has healed, the device may be removed using conventional access procedures. During such removal, a tool may be introduced to activate the actuator and direct the splines back to the collapsed state before removal from the bone.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.